U.S. Sen. Mark Kirk is demanding criminal background checks on the unaccompanied children that have crossed the U.S. border with Mexico.

According to Kirk, 429 unaccompanied minors are living in Chicago.

The Illinois Republican says he’s sent letters to the U.S. ambassadors to Guatemala, Honduras and El Salvador asking whether their embassies have performed criminal background checks. He says the federal government must ensure the immigrants “pose no threat.”